JPS6233268B2 - - Google Patents

Description

[Detailed description of the invention]

A. Field of Industrial Application The present invention relates to a phosphor that emits light when stimulated by X-rays, and mainly relates to a phosphor used in an X-ray intensifying screen. B. Prior Art Fluorescent materials that emit light when stimulated by X-rays are mainly used in X-ray intensifying screens. X-ray intensifying screens are generally used in combination with photographic film to enhance the X-ray image of a subject. The phosphor used in such an X-ray intensifying screen is required to have a large amount of X-ray absorption, high luminous efficiency, and weak afterglow component. An X-ray intensifying screen coated with a phosphor that absorbs a large amount of X-rays can improve the sharpness and density resolution of X-ray images, thereby improving image quality. A phosphor with high luminous efficiency can be used with less X-ray irradiation, and a phosphor with less afterglow component can prevent adverse effects caused by afterimages. Conventional phosphors with excellent image quality
In recent years, instead of _CaWO4 , _Gd2O2S : _Tb , BaFCl:
Fluorescent materials such as Eu, LaOBr:Tm, and YTaO ₄ :Tm have been put into practical use. However, because Gd ₂ O ₂ S:Tb is used in combination with orthofilm, which emits green light and is sensitive in the blue to green region, the film is easily exposed to light in the darkroom, and the darkroom lamp must be dimmed. Poor workability. BaFCl:Eu and LaOBr:Tm have a small amount of X-ray absorption, and their particle shapes cause a lot of scattering of light generated by X-rays, so they inevitably degrade the quality of X-ray images. YTaO ₄ :Tm phosphor has a large amount of X-ray absorption and high luminous efficiency. Furthermore, because of the polyhedral grain shape, there is less light scattering and the quality of the X-ray image is good. Furthermore, since it emits blue light, it can be used in combination with a regular film that is sensitive to the blue region, so the film is less likely to be exposed to light from a darkroom lamp, making it easier to work in a darkroom by making the darkroom lamp brighter. YTaO ₄ :Tm phosphors having such characteristics are considered promising as phosphors for intensifying screens. but,
Compared to other fluorophores, this YTaO ₄ :Tm fluorophore has
It has the disadvantage of a strong afterglow component, which limits its uses. If a YTaO ₄ :Tm phosphor with a weak afterglow component could be developed, it would be possible to create a phosphor with ideal characteristics for X-rays. The present invention was developed to achieve this goal, and the important purpose of the present invention is to have a large amount of X-ray absorption, high luminous efficiency, and to weaken the afterglow component. The object of the present invention is to provide a phosphor that emits light. In addition, another important object of the present invention is that it is possible to increase the luminous efficiency at a specific content.
The object of the present invention is to provide a phosphor that emits light when stimulated by X-rays. C. Means for Solving Conventional Problems In order to achieve the above object, the present inventor conducted various studies on rare earth tantalate phosphors and rare earth niobate phosphors. the result,
By incorporating at least one type of divalent metal among Be, Mg, Ca, Sr, Ba, Zn, and Cd into the phosphor in a specific range, we succeeded in significantly improving its afterglow properties. did. Furthermore, the phosphor obtained by containing a specific amount of divalent metal not only had significantly improved afterglow properties, but also was able to significantly improve luminous efficiency. That is, the phosphor of the present invention has a composition formula (): M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ () (where M is Be, Mg, Ca, Sr, Ba, Zn,
At least one divalent metal selected from the group of Cd, and Ln is at least one of Y, Gd, La, and Lu.
is a seed element, D contains either or both of Ta and Nb, and a and x are each 1×10 ^-5
It is a numerical value in the range of ≦a≦1, 0≦x≦0.03). When the amount of M mixed in the phosphor is large, the afterglow properties are improved, but when it is too large, the luminous efficiency decreases. Furthermore, if the amount of Tm ³⁺ as an activator is too large, the luminous efficiency will decrease. However, since the phosphor of the present invention also emits light itself, the active agent Tm ³⁺
It is also possible to use it without containing it at all. D Functions and Effects The phosphor of the present invention represented by the above compositional formula () exhibits significantly improved afterglow properties in addition to having excellent X-ray absorption properties and luminous efficiency.
Furthermore, by adjusting the content of each element within a specific range, it is possible to achieve higher luminance than conventional phosphors. Therefore, by using the phosphor represented by the above compositional formula () in an X-ray intensifying screen, it is possible to constantly obtain images with excellent image quality and less noise due to afterglow. , it is also possible to improve the sensitivity of X-ray images. The features of the present invention will be explained in detail with reference to FIGS. 1 to 4. In Fig. 1, curve C represents the composition formula, M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ , where M is
Ca, Ln is Y, D is Ta, a=1×10 ^-4 , x=0.005
In the case of Ca _0.0001 Y _0.994933 TaO ₄ :0.005Tm ³⁺ , the afterglow characteristic of the phosphor is shown. For comparison, the conventional a=0
Curve A shows the afterglow characteristic of the phosphor in the case of Y _0.995 TaO ₄ :0.005Tm ³⁺ . In Figure 1, the vertical axis shows the relative afterglow amount (logarithm of [light emission amount after a certain period of time/light emission amount during X-ray stimulation]);
The horizontal axis shows the afterglow decay time (time elapsed after X-ray irradiation was stopped). According to FIG. 1, it can be seen that the phosphor of the present invention in which a=1×10 ^-4 has a significantly superior afterglow property as compared to the conventional phosphor in which a=0. Furthermore, in FIG. 1, in the above compositional formula () M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ , M is Ca,
Ln is Y, D is Ta, X=0.005, a=1×
10 ^-5 , a=1×10 ^-2 , a=1×10 ^-1 , that is, Ca _0.00001 Y _0.9949933 TaO ₄ :0.005Tm ³⁺ ,
Ca _0.01 Y _0.9883 TaO ₄ : 0.005Tm ³⁺ and
The afterglow characteristics of the phosphor Ca _0.1 Y _0.9283 TaO ₄ :0.005Tm ³⁺ are shown in order by curves B, D, and E. According to this figure, a=1×10 ^-2 , a=1×10 ^-1
It is clear that the phosphor of the present invention has particularly excellent afterglow characteristics as compared to the conventional phosphor in which a=0. Next, the phosphor of the present invention Ca _{Y 0 .995-(2/3)a} TaO ₄ :
Taking 0.005Tm ³⁺ as an example, the influence of calcium content on luminescence properties will be explained based on FIG. 2. In FIG. 2, the vertical axis shows the brightness (relative value) when emitted by X-ray stimulation, and the horizontal axis shows the value of the amount of calcium a contained in the phosphor. According to FIG. 2, in the above compositional formula, 2×
The luminous efficiency was significantly improved when 10 ^-3 ≦a≦30×10 ^-3 , and a luminance improvement of up to 30% was obtained compared to a=0, that is, one containing no calcium. Next, taking the phosphor of the present invention Sra _{Y 0 .995-(2/3)a} TaO ₄ :0.005Tm ³⁺ as an example,
The influence of strontium content on afterglow characteristics and luminescence characteristics will be explained with reference to FIGS. 3 and 4. Figure 3 shows Sr _a Y _{0.995- (2/3)a} TaO ₄ :0.005Tm ³⁺
This shows the influence of the styrontium content (a value) of the phosphor on the afterglow characteristics. In that order, a=0, a=1×10 ^-5 , a=5
×10 ^-5 , a=1×10 ^-4 , a=2×10 ^-3 , a=1×
10 ^-2 , which shows the afterglow characteristics of the phosphor. As is clear from this figure, the value of a is 1×10 ^-5
The afterglow properties were significantly improved. Furthermore, as is clear from the luminescence characteristics shown in Fig _{. 4} , ^the Sr _a Y ₀ . When it exceeds ×10 ^-4 , the relative brightness also increases significantly, and compared to a = 0, that is, strontium-free,
In the range of ×10 ^-4 ≦a≦60×10 ^-4 , 50% to
An 80% brightness improvement was confirmed. Such a tendency shown in FIGS. 1 to 4 appears similarly even when M is attached to Be, Mg, Ba, Zn, or Cd in the composition formula, and the afterglow characteristics and brightness can be improved. In addition, in the composition formula, M is Be, Mg, Ca, Sr,
In the case of two or more types of Ba, Zn, and Cd, the first
The trends shown in Figures 4 to 4 appear. However, in the measurements shown in Figures 1 to 4, the brightness of the phosphor is measured by irradiating the phosphor with X-rays and transmitting the emitted light from the phosphor through a filter with the characteristics shown in Figure 5. After that, the photomultiplier was irradiated, and the luminous intensity was then converted to current, and the magnitude of the output current was compared. FIG. 6 shows the sensitivity characteristics of the photomultiplier. E Preferred Examples Examples of the present invention will be described below. However, these examples do not limit the present invention. Example 1 112.3g of yttrium oxide, thulium oxide
Dissolve 0.965g in 340ml of 10N hydrochloric acid, add pure water to make 1000ml, and heat to 80°C with stirring. On the other hand, an oxalic acid aqueous solution prepared by dissolving 220 g of oxalic acid in 1000 ml of pure water is heated to 80°C, and added to the hydrochloric acid solution heated to 80°C while stirring. Thus, yttrium and thulium oxalates are produced and co-precipitated in the mixed solution. Next, the solution containing the precipitate is allowed to cool, and then washed with pure water five times by decantation, and the precipitate is suction-filtered. This precipitate was thermally decomposed at 850° C. for 3 hours to convert the oxalate into an oxide, yielding 113.2 g. After thoroughly mixing 64.1 g of the oxide thus obtained, 125 g of tantalum pentoxide, and 21 g of calcium chloride, the mixture was filled into an aluminium crucible and heated at 1000℃.
Bake for 15 hours. This sintered body contains lithium chloride 62.5
g Add 0.4g of boric acid and mix by pulverizing with a ball mill. Next, the obtained mixture is filled into an alumina crucible, calcined at 1200° C. for 10 hours, pulverized in a ball mill, washed 5 times with pure water by decantation, and suction filtered. Furthermore, this at 120℃
Dry for 15 hours. It was confirmed that the compositional formula of the phosphor thus obtained could be expressed as Ca _0.01 Y _0.9883 TaO ₄ :0.005Tm ³⁺ . The afterglow of this phosphor was extremely lower than that of conventional products that do not contain calcium. (Figure 1) Also, the relative brightness was improved by 30% compared to a comparative product that does not contain calcium. (Figure 2) Next, using this phosphor, an X-ray intensifying screen was made in the following manner. Methyl ethyl ketone was added to a mixture of phosphor particles and linear polyester resin, and nitrocellulose with a degree of nitrification of 11.5% was further added to prepare a phosphor dispersion. After adding diethyl phthalate, phthalic acid, and methyl ethyl ketone to this dispersion, they were thoroughly stirred and mixed using a homogenizer, so that the mixing ratio of binder and phosphor was 1:20 (weight ratio), and the viscosity was 30 PS (25 ℃) coating solution was prepared. This coating solution was uniformly applied using a doctor blade onto a polyester sheet (support, thickness 200 μm) containing titanium dioxide placed horizontally on a glass plate. After coating, the support on which the coating was formed was dried in a dryer to form a phosphor layer with a thickness of 180 μm on the support. Then, a polyethylene transparent film was adhered onto this phosphor layer using a polyester adhesive to form a transparent protective film (thickness: 10 μm), thereby making an intensifying screen. The sensitivity of this intensifying screen was improved by 30% compared to one that did not contain calcium, and furthermore, the sensitivity of the film due to afterglow was eliminated. Example 2 63.6g of yttrium oxide, thulium oxide
0.456g, 125g of tantalum pentoxide, and 29g of strontium chloride.Other methods were as described in Example 1.
A phosphor having a compositional formula of Sr _0.002Y0.9937 TaO ₄ :0.005Tm ³⁺ was obtained. This phosphor has a significantly weaker afterglow component than conventional products that do not contain strontium. (Figure 3) Also, the relative brightness was improved by 80% compared to a comparative product that does not contain strontium. (Figure 4) When this phosphor is used in an X-ray intensifying screen, compared to one that does not contain strontium,
It was confirmed that the sensitivity was improved by 80% and the afterglow characteristics were also significantly superior. Example 3 63.8g of yttrium oxide, thulium oxide
0.218g, tantalum pentoxide 125g, and magnesium chloride 1.1g.Other methods are as in Example 1.
A phosphor was manufactured in the same manner as above to obtain a phosphor having a compositional formula of Mg _0.06 Y _0.958 TaO ₄ :0.002Tm ³⁺ . The relative brightness and relative afterglow of this phosphor are as follows: Conventional product 3 (compositional formula, Y _0.998) , which does not contain Mg
₉₈ TaO ₄ :0.002Tm ³⁺ ), the photometric results shown in Table 1 were shown. In Table 1, the relative afterglow amount is Log[30
Afterglow amount after seconds/light emission amount].

[Table] Example 4 63.8g of yttrium oxide, thulium oxide
A phosphor was produced in the same manner as in Example 1 using 0.218 g of tantalum pentoxide, ₁₂₅ g of _{tantalum pentoxide} , and ¹⁷ g of barium chloride. I got a body. The relative brightness and relative afterglow amount of this phosphor are
Conventional product 4 that does not contain Ba (compositional formula, Y _0.998
TaO ₄ :0.002Tm ⁺³ ), the photometric results shown in Table 2 were shown.

[Table] Example 5 99.1g of gadolinium oxide, thulium oxide
0.328g, tantalum pentoxide 125g, and beryllium oxide 0.71g, otherwise the phosphor was manufactured in the same manner as in Example 1, and the composition formula: Be _0.005 Gd _0.9937 TaO ₄ :0.003Tm ³⁺ A phosphor with , was obtained. The relative brightness and relative afterglow amount of this phosphor are as follows: Conventional product 5 (compositional formula,
Gd _0.997 TaO ₄ :0.003Tm ⁺³ ), the photometric results shown in Table 3 were shown.

[Table] Example 6 31.7 g of yttrium oxide, 50.9 g of gadolinium oxide, 0.546 g of thulium oxide, 125 g of tantalum pentoxide, and 0.71 g of zinc carbonate were used, and the other methods were the same as in Example 1. A phosphor having the compositional formula Zn _0.01 Y _0.49415 Gd _0.49415 TaO ₄ :0.005Tm ³⁺ was obtained. The relative brightness and relative afterglow amount of this phosphor are as shown in the photometric results shown in Table 4 compared to conventional product 6 (compositional formula, Y _0.4975 Gd _0.4975 TaO ₄ :0.005Tm ⁺³ ) which does not contain Zn. Ta.

[Table] Example 7 31.7g of yttrium oxide, lanthanum oxide
A phosphor was produced using the same method as in Example 1 except that 45.8 g of thulium oxide, 0.546 g of thulium oxide, 125 g of tantalum pentoxide, and 0.98 g of cadmium carbonate were used, and the composition formula was Cd _0.01 Y _0.49415 La. A phosphor with _0.49415 TaO ₄ :0.005Tm ³⁺ was obtained. The relative brightness and relative afterglow amount of this phosphor are as shown in the photometric results shown in Table 5 compared to conventional product 7 (compositional formula, Y _0.4975 La _0.4975 TaO ₄ :0.005Tm ⁺³ ) which does not contain Cd. Ta.

[Table] Example 8 63.6g of yttrium oxide, thulium oxide
A phosphor was produced using the same method as in Example 1 except that 0.456 g, 124.4 g of tantalum pentoxide, 0.376 g of niobium pentoxide, and 29 g of strontium chloride were used, and the composition formula was Sr _0.002 Y _0.9937. Ta _0.995 Nb _0.005 O ₄ :0.005Tm ³⁺
A phosphor was obtained. The relative brightness and relative afterglow _of this phosphor are as shown in Table 6, compared to conventional product 8 (compositional formula, Y _0.995 Ta _0.995 Nb _0.005 O ₄ :0.005Tm ⁺³ ) that does not contain Sr. The results were shown.

[Table] In the above compositional formula, the phosphor of the present invention has Ln
Lu can also be used instead of Y, Gd, and La shown in Examples 1 to 8. Since the phosphor of the present invention also emits light itself,
It is also possible to use it without containing any active agent Tm ³⁺ . In the phosphor of the present invention whose matrix emits light, Pr, Sm, Eu, Tb, Dy, Yb, etc. can be used as ^{an active agent in addition to or in place of Tm 3+ .} By the way, the phosphor of the present invention can be used in all applications where it emits light when stimulated by X-rays, but it is mainly used in X-ray intensifying screens. Therefore, specific examples in which the phosphor of the present invention is used in an X-ray intensifying screen will be described in detail below. An X-ray intensifying screen basically consists of a support and a phosphor layer provided thereon, and the phosphor layer is a phosphor represented by the above composition formula (1). It consists of a binder containing and supporting the following in a dispersed state. The phosphor layer can be formed on the support by the following known method. First, a phosphor represented by the above compositional formula (1) and a binder are added to a solvent and mixed to prepare a coating solution in which phosphor particles are uniformly dispersed in the binder solution. . Examples of binders for the phosphor layer include nitrocellulose, polyalkyl (meth)acrylates, linear polyesters and mixtures thereof. Examples of solvents for preparing the coating solution include esters of lower fatty acids and lower alcohols such as ethyl acetate and butyl acetate, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane and ethylene glycol monoethyl ether, and mixtures thereof. can be mentioned. The mixing ratio of the binder and the phosphor in the coating solution varies depending on the characteristics of the intended intensifying screen, the particle size of the phosphor, etc., but in general, the mixing ratio of the binder and the phosphor is is preferably selected from 1:8 to 1:40 (weight ratio). The coating solution also contains a dispersant for improving the dispersibility of the phosphor particles in the coating solution, and a bond between the binder and the phosphor particles in the phosphor layer after formation. Additives such as plasticizers for improving strength may be mixed. The coating liquid prepared as described above is uniformly applied to the surface of the support using a conventional coating means such as a doctor blade, roll coater, knife coater, etc., so that the coating film after coating is coated. form. After the coating film is formed, the coating film is dried to complete the formation of the phosphor layer on the support. The thickness of the phosphor layer varies depending on the characteristics of the intended intensifying screen, the particle size of the phosphor, the mixing ratio of binder and phosphor, etc., but is usually selected from the range of 70 μm to 700 μm. is preferred. Note that the number of phosphor layers may be one, or two or more. If laminated, at least one of them
The layer contains a phosphor having the composition formula (1) above. The support can be arbitrarily selected from various materials known as supports for intensifying screens. Examples of such materials include films of plastic materials such as cellulose acetate, polyester, polyamide, polycarbonate, metal sheets such as aluminum sheets, aluminum alloy sheets, pigmented papers containing titanium dioxide, etc. . In addition, when using plastic film,
A light-absorbing substance such as carbon black may be incorporated, or a light-reflecting substance such as titanium dioxide may be incorporated. The former is a support suitable for a high sharpness type intensifying screen, and the latter is a support suitable for a high sensitivity type intensifying screen. In a typical X-ray intensifying screen, a transparent protective film for physically and chemically protecting the phosphor layer is provided on the surface of the phosphor layer on the opposite side that is in contact with the support. It is preferable to provide such a transparent protective film also to an intensifying screen in which the phosphor of the present invention is used. The transparent protective film is made of, for example, a cellulose derivative such as cellulose acetate or nitrocellulose, or
polymethyl methacrylate, polycarbonate,
It can be formed by dissolving a transparent polymeric substance such as polyvinyl acetate in an appropriate solvent and applying a solution prepared on the surface of the phosphor layer. Alternatively, it can also be formed by a method in which a transparent thin film separately formed from polyethylene, polyethylene terephthalate, polyamide, etc. is adhered to the surface of the phosphor layer using a suitable adhesive.

[Brief explanation of the drawing]

Figures 1 and 3 are graphs showing the afterglow characteristics of luminescent materials that emit light when stimulated by X-rays, and Figures 2 and 4 are graphs showing the relative brightness of phosphors with varying values of a in the composition formula. FIG. 5 is a characteristic diagram of a filter used to measure the luminance of the phosphor, and FIG. 6 is a sensitivity characteristic diagram of a photomultiplier used to measure the luminance of the phosphor.

Claims (1)

[Claims] 1 Compositional formula () M _a Ln _1-x-(2/3)a DO ₄ :xTm ³⁺ () (However, M is Be, Mg, Ca, Sr, Ba, Zn,
at least one divalent metal selected from the group of Cd; Ln is at least one element of Y, Gd, La, and Lu; D includes either or both of Ta and Nb; a and x is 1×10 ^-5 ≦
A phosphor that emits light when stimulated by X-rays, expressed as follows: a≦1, 0≦x≦0.03. 2. The phosphor that emits light when stimulated by X-rays according to claim 1, wherein M is Ca and a is 1×10 ⁻⁵ ≦a≦1×10 ⁻¹ . 3. A phosphor that emits light when stimulated by X-rays according to claim 1, wherein M is Sr and a is 1×10 ⁻⁵ ≦a≦1×10 ⁻² .